The goal of the proposed studies is to understand the molecular details responsible for the transport and targeting of secretory products via the actin cytoskeleton. Current results suggest that secretory vesicles are transported down actin cables by a myosin V. The proposed experiments explore how transport is affected in mutants with altered polarity and what features of the actin cytoskeleton are required to allow it to function as a myosin V substrate. Four specific aims are presented: (1) to develop a system for the localization of the sites of emergence of secretory products; (2) to produce temperature sensitive tropomyosin (tpm1) mutants that will be used to investigate polarization and depolarization of the actin cytoskeleton and secretory processes; (3) to screen for mutant that have a tpm1 sensitive secretory defect; and (4) to identify proteins that interact with the myosin V tail by biochemical and genetic approaches.